1. Field of the Invention
The present invention relates, generally, to a heat exchanger for a refrigeration/air conditioning system. More particularly, the present invention relates to a single tank evaporator core heat exchanger in an air conditioning system for an automotive vehicle.
2. Description of the Related Art
Plate-fin heat exchangers are well known in the art. In these types of heat exchangers, a plurality of elongated plates are joined together, such as through brazing or a lamination process to define a plurality of passageways for the movement of a fluid therethrough. Each of the passageways is formed by the inwardly facing surface of a pair of joined plates so as to form a flat tube. The passageways are interconnected so that a fluid may flow through the plurality of joined plates forming the heat exchanger. The joined plates also define central fluid conducting sections or "tanks" as they are commonly known in the art. The heat exchanger may employ a single tank disposed on one end thereof or a pair of tanks disposed at opposite ends of the evaporator core. As is also known in the art, conductive fin strips are located between outwardly facing surfaces of the pair of joined plates. Heat exchangers of this type have particular utility as evaporators for air conditioning systems of motor vehicles.
Typically, plate-fin heat exchangers are manufactured by stacking a plurality of individual plate together to form a flat tube and interleaving fin members between each tube. Endsheets are then placed on opposite ends of the heat exchanger to form a heat exchanger core. An inlet and outlet manifold are then inserted into an aperture formed in the endsheet or tank to provide for fluid communication into and out of the evaporator. The core is braised in a furnace to complete the manufacturing process.
In automotive applications, space is always at a premium and therefore the size configuration or "packaging" of the heat exchanger is an important consideration. To that end, it has been found that evaporator cores having a single tank are more efficient than dual tank designs. This is because the effective face area or the amount of space in the overall package of the heat exchanger dedicated to the passageways can be maximized in a single tank design thus increasing the heat transfer efficiency. In addition, and among single tank heat exchanger designs, efforts have been made to further maximize their efficiency. For example, single tank designs having three separate refrigerant flow tunnels in the tank have been employed in the past. Each plate is formed with two cups which, when joined to a confronting plate, form two flow tunnels. A tubular manifold extending through an aligned aperture in the plates may be employed for either the inlet or outlet to form the other or third flow tunnel in the tank. Such manifolds require additional brazing between the tubular manifold and the plates to secure the manifold within the evaporator core. This involves an additional step in the manufacturing process and may possibly result in leakage if a good brazed joint is not formed.
Other designs have been proposed wherein the tubular manifold is eliminated and another or third cup is formed in each plate, aligned side-by-side such that the centerline of the aperture extending through each flow tunnel is contained in the same plane. However, in practice it has been found impractical to manufacture such single tank, three cup heat exchangers while maintaining optimum size and packaging considerations. This is because of the limitation of the ductility of the plates. More specifically, during the manufacturing process, the material in and surrounding the cups is thinned as it is drawn during the stamping process to such an extent that the heat exchanger may fail at the tanks when subjected to elevated pressures. Further, the plates may fail or break at the stamping stage due to extreme draws in the stamped plate. However, spacing the cups relative to one another laterally across the plate is unacceptable because this increases the width of the heat exchanger thereby increasing the overall package of the evaporator core.
Accordingly, it would be advantageous to provide a single tank evaporator core having three cups which eliminates the need for a separate tubular manifold brazed to successive plates to serve as an inlet or outlet. Furthermore, it would be advantageous to provide a single tank evaporator core which may be consistently manufactured and which reaches failure at the cups in the tank due to thinning or breakage of the plate material.